Method and circuit for transferring data stream across multiple clock domains

ABSTRACT

The method and circuit provide an effective implementation to handle the data transferring problem between multiple clock domains. A shift circuit shifts the incoming data stream and a sampling module sequentially samples and outputs each signal in the first group signals and the second group signals by the N sampling pulses with a sequence.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and circuit for transferring data, and more especially, to a method and circuit for transferring data stream across multiple clock domains.

2. Background of the Related Art

It's quite common to transfer data stream in multiple clock domains in the electronic circuit. For example, referring to FIG. 1A, it depicts a circuit for transferring data in three clock domains. The data stream data_0 10 in domain D 14 is first sampled by sampling pulse clk1 17 to become data stream data_1 11 in domain D+1 15, thereafter, the data stream data_2 12 is then sampled by sampling pulse clk2 18 to become the data stream data_3 13 in domain D+2 16, and so on.

Moreover, even though the frequency for all sampling clocks are the same, the skew and jitter may still happen around the sampling edges of different clocks (as shown in FIG. 1B, there is skew or jitter happened on the rising or falling edge of sampling pulse clk2 18, even the frequency of sampling pulse clk1 17 is equal to that of sampling pulse clk2 18) and such the skew or jitter causes the phase difference and sampling ambiguity.

However, since the frequency of sampling pulse clk1 17, clk2 18, and clk3 19 may be different, it is likely to generate sampling ambiguity among sampling processes. For example, as shown in FIG. 2, when a first data stream with several frames (K−1, K, K+1, each of which comprises 3 parallel bits) originally sampled by sampling pulse clk 1 may be sampled by a faster sampling pulse clk 2 to become a second data stream in series format and then to be transmitted through high speed series transmission line (ex, LVDS). The traditional solution to reduce the sampling ambiguity in this situation is using three different clocks sel_0, sel_1, and sel_2 to respectively sample the data 0, data 1, and data 2 in the frame K. Besides, It may happen that, due to the skew or jitter, the clock sel_0 samples somewhere at the edge of sampling pulse clk1 and then still causes sampling ambiguity.

SUMMARY OF THE INVENTION

In order to solve the problems mentioned above, the method provides a skew-tolerance method and circuit for transferring digital data stream through multiple domains in an electrical circuit, such as computing system.

In a preferred exemplary embodiment of present invention, a method for transferring a data stream with N parallel signals from a first clock domain to a second clock domain, the N parallel signals having a first group parallel signals and a second group parallel signals, the N parallel signals being corresponding to a N sampling pulses with a first sequence, the method including: shifting the second group parallel signal; and sequentially sampling and outputting each signal in the first group parallel signals and the shifted second group digital signals by the N sampling pulses with a second sequence, wherein the second sequence is different from the first sequence.

Accordingly, one embodiment of the present invention is a circuit for transferring a data stream with N parallel signals from a first clock domain to a second clock domain, the N parallel signals having a first group parallel signals and a second group parallel signals, the N parallel signals being corresponding to a N sampling pulses with a first sequence, the circuit including: a shifting circuit for shifting the second group parallel signals; and a sampling module for sequentially sampling and outputting each signal in the first group parallel signals and the shifted second group digital signals by the N sampling pulses with a second sequence, wherein the second sequence is different from the first sequence.

Furthermore, another embodiment of the present invention provides A method for transferring a set of (Q*N) serial digital data from a first clock domain with a first sampling clock to a second clock domain with a second sampling clock, the method including: dividing the set of (Q*N) serial digital data and generating Q digital data streams; and sequentially transferring the Q digital data streams to the second clock domain, each digital data stream including N parallel signals with a first group parallel signals and a second group parallel signals, the N parallel signals being corresponding to a N sampling pulses with a first sequence, each digital data stream being transferred by the following steps: shifting the second group parallel signal; and sequentially sampling and outputting each signal in the first group parallel signals and the shifted second group digital signals by the N sampling pulses with a second sequence, wherein the second sequence is different from the first sequence.

Accordingly, one embodiment of the present invention is a circuit for transferring a set of (Q*N) serial digital data from a first clock domain with a first sampling clock to a second clock domain with a second sampling clock, the circuit including: a divider for dividing the set of (Q*N) serial digital data and generating Q digital data streams; and a transmitter for sequentially transferring each of the Q digital data streams to the second clock domain, each digital data stream including N parallel signals with a first group parallel signals and a second group parallel signals, the N parallel signals being corresponding to a N sampling pulses with a first sequence, the transmitter comprising: a shifting circuit for shifting the second group parallel signals; and a sampling module for sequentially sampling and outputting each signal in the first group parallel signals and the shifted second group digital signals by the N sampling pulses with a second sequence, wherein the second sequence is different from the first sequence.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram of circuit for transferring data in three clock domains of prior art.

FIG. 1B is a timing diagram of sampling clocks in the circuit of FIG. 1A.

FIG. 2 is a timing diagram transferring data bits in prior art.

FIG. 3 is a method for transferring a data stream with N parallel signals from a first clock domain to a second clock domain in accordance with one embodiment of the present invention.

FIG. 4 is a circuit for transferring a data stream with N parallel signals from a first clock domain to a second clock domain in accordance with one embodiment of the present invention.

FIG. 5 is a method for transferring a data stream with N parallel signals from a first clock domain to a second clock domain in accordance with one embodiment of the present invention.

FIG. 6 is a circuit for transferring a data stream with N parallel signals from a first clock domain to a second clock domain in accordance with one embodiment of the present invention.

FIG. 7A is a block diagram of circuit for transferring data in multiple domains in accordance with one embodiment of the present invention.

FIG. 7B is a timing diagram of sampling pulses in FIG. 3A in accordance with an embodiment of the present invention.

FIG. 8 is a flow chart of the method in accordance with an embodiment of the present invention.

FIG. 9 is a block diagram of circuit in accordance with one embodiment of the present invention.

FIG. 10 is a timing diagram of sampling pulses in FIG. 5 in accordance with an embodiment of the present invention.

FIG. 11 is a flow chart of the method in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides the method and circuit for transferring the data stream across different clock domains to avoid the problem of sampling ambiguity.

Referring to FIG. 3 is a method for transferring a data stream with N parallel signals from a first clock domain to a second clock domain. The N parallel signals include a first group parallel signals and a second group parallel signals, and the N parallel signals are corresponding to a N sampling pulses with a first sequence. The first sequence of N sampling pulses is from first to a (M−1)th sampling pulse and from the Mth to the Nth sampling pulse, M is a predetermined integral. In step S11 the second group parallel signal is shifted; and step S12 each signal in the first group parallel signals and the shifted second group digital signals are sampled and output sequentially by the N sampling pulses with a second sequence. The second sequence of N sampling pulses is the Mth to the Nth sampling pulses and the first to the (M−1)th sampling pulses. The second sequence is different from the first sequence.

In one embodiment according to the present invention in step S11 of FIG. 3, the second group parallel signals have S parallel signals, and each signal in the second group parallel signals is shifted I times one clock cycle of the second clock domain, I is a predetermined integral. The first group parallel signals have (N−S) parallel signals. In the step S12 each signal in the first group parallel signals is shifted before sampling. The Lth parallel signal in the first group parallel signals is shifted (L−1) times one clock cycle in the second clock domain and L is an integral between 1 and (N−S).

In another embodiment according to the present invention in step S11 of FIG. 3, the second group parallel signals have S parallel signals and each signal in the second group parallel signals is shifted. The Kth parallel signal in the second group parallel signals is shifted (K+I−1) times one clock cycle of the second clock domain, I is a predetermined integral and K is an integral between 1 and S. In step S12, the first group parallel signals have (N−S) parallel signals and each signal in the first group parallel signals is shifted before sampling. The Lth parallel signal in the first group parallel signals is shifted (L−1) times one clock cycle of the second clock domain and L is an integral between 1 and (N−S).

The FIG. 4 illustrates a circuit diagram for transferring a data stream with N parallel signals from a first clock domain to a second clock domain according FIG. 3. The N parallel signals have a first group of parallel signals and a second group of parallel signals, and the N parallel signals are corresponding to the N sampling pulses with a first sequence. The circuit includes: a shifting circuit 111 for shifting the second group parallel signals; and a sampling module 112 for sequentially sampling and outputting each signal in the first group parallel signals and the shifted second group digital signals by the N sampling pulses with a second sequence, which is different from the first sequence. The first sequence of N sampling pulses is the first to the (M−1)th sampling pulses and the Mth to the Nth sampling pulses. The second sequence of N sampling pulses is the Mth to the Nth sampling pulses and the first to the (M−1)th sampling pulses, M is a first predetermined integral.

In one embodiment according to the present invention in FIG. 4, the second group parallel signals have S parallel signals and the shifting circuit 111 includes a plurality of gates corresponding to the second group parallel signals. Each gate is controlled by an Ith sampling pulse of the N sampling pulses and shifts the corresponding parallel signal I times one clock cycle of the second clock domain, I is a predetermined integral. The first group parallel signals have (N−S) parallel signals. The shifting circuit 111 further includes a plurality of gates for shifting the first group parallel signals. The Lth gate corresponding to the Lth parallel signal in the first group parallel signals is controlled by a (L−1)th sampling pulse of the N sampling pulses, and the Lth gate shifts the corresponding Lth parallel signal (L−1) times one clock cycle of the second clock domain. The L is an integral between 1 and (N−S).

In another embodiment according to the present invention in FIG. 4, the second group parallel signals have S parallel signals. The shifting circuit 111 includes a plurality of gates corresponding to the second group parallel signals. The Kth gate of the second plurality of gates is controlled by an (K+I−1)th sampling pulse of the N sampling pulses and shifts the corresponding parallel signal (K+I−1) times one clock cycle of the second clock domain. The I is a predetermined integral and the K is an integral between 1 and S. The first group parallel signals have (N−S) parallel signals. The shifting circuit 111 includes another plurality of gates for shifting the first group parallel signals. The Lth gate corresponding to a Lth parallel signal in the first group parallel signals is controlled by a (L−1)th sampling pulse of the N sampling pulses, and the Lth gate shifts the corresponding Lth parallel signal (L−1) times one clock cycle of the second clock domain, L is an integral between 1 and (N−S).

Referring to FIG. 5 is a method for transferring a set of (Q*N) serial digital data from a first clock domain with a first sampling clock to a second clock domain with a second sampling clock. In step S21 dividing the set of (Q*N) serial digital data and generating Q digital data streams; and step S22 sequentially transferring the Q digital data streams to the second clock domain, each digital data stream including N parallel signals with a first group parallel signals and a second group parallel signals, and each N parallel signals is corresponding to a N sampling pulses with a first sequence. Each digital data stream is transferred by shifting the second group parallel signal, and sequentially sampling and outputting each signal in the first group parallel signals and the shifted second group digital signals by the N sampling pulses with a second sequence, which is different from the first sequence. The first sequence of N sampling pulses is the first to the (M−1)th sampling pulses and the Mth to the Nth sampling pulses, the second sequence of N sampling pulses is the Mth to the Nth sampling pulses and the first to the (M−1)th sampling pulses, M is a predetermined integral.

In one embodiment according to the present invention in step S22, the second group parallel signals have S parallel signals, and each signal in the second group parallel signals is shifted amount equal to I times one clock cycle of the second clock domain. The I is a predetermined integral, and the first group parallel signals have (N−S) parallel signals. In the step S22 each signal in the first group parallel signals is shifted before sample the same. The Lth parallel signal in the first group parallel signals is shifted amount equal to (L−1) times one clock cycle in the second clock domain and L is an integral between 1 and (N−S).

In another embodiment according to the present invention in step S22, the second group parallel signals have S parallel signals and each signal in the second group parallel signals is shifted. The Kth parallel signal in the second group parallel signals is shifted amount equal to (K+I−1) times one clock cycle of the second clock domain. The I is a predetermined integral and K is an integral between 1 and S. In step S22, the first group parallel signals have (N−S) parallel signals and each signal in the first group parallel signals is shifted before sampling. The Lth parallel signal in the first group parallel signals is shifted amount equal to (L−1) times one clock cycle of the second clock domain and L is an integral between 1 and (N−S).

The FIG. 6 illustrates a circuit diagram for transferring a set of (Q*N) serial digital data from a first clock domain with a first sampling clock to a second clock domain with a second sampling clock, the circuit includes: a divider 130 for dividing the set of (Q*N) serial digital data and generating Q digital data streams; and a transmitter 120 for sequentially transferring each of the Q digital data streams to the second clock domain. Each digital data stream including N parallel signals with a first group parallel signals and a second group parallel signals, the N parallel signals is corresponding to a N sampling pulses with a first sequence. In addition, the transmitter has a shifting circuit 121 for shifting the second group parallel signals, and a sampling module 122 for sequentially sampling and outputting each signal in the first group parallel signals and the shifted second group digital signals by the N sampling pulses with a second sequence, which is different from the first sequence. The first sequence of N sampling pulses is a first to a (M−1)th sampling pulses and a Mth to a Nth sampling pulses, the second sequence of N sampling pulses is the Mth to the Nth sampling pulses and the first to the (M−1)th sampling pulses, M is a predetermined integral.

In one embodiment according to the present invention in FIG. 6, the second group parallel signals have S parallel signals and the shifting circuit 121 includes a plurality of gates corresponding to the second group parallel signals. Each gate is controlled by an Ith sampling pulse of the N sampling pulses and each gate shifts the corresponding parallel signal I times one clock cycle of the second clock domain. The I is a second predetermined integral and the first group parallel signals have (N−S) parallel signals. The shifting circuit 121 further includes another plurality of gates for shifting the first group parallel signals. The Lth gate in the plurality of gates corresponding to a Lth parallel signal in the first group parallel signals is controlled by a (L−1)th sampling pulse of the N sampling pulses, and the Lth gate shifts the corresponding Lth parallel signal (L−1) times one clock cycle of the second clock domain. The L is an integral between 1 and (N−S).

In another embodiment according to the present invention in FIG. 6, the second group parallel signals have S parallel signals. The shifting circuit 121 including a plurality of gates corresponding to the second group parallel signals, wherein a Kth gate of the plurality of gates is controlled by an (K+I−1)th sampling pulse of the N sampling pulses and the Kth gate shifts the corresponding parallel signal (K+I−1) times one clock cycle of the second clock domain. The I is a predetermined integral and the K is an integral between 1 and S, the first group parallel signals having (N−S) parallel signals, the shifting circuit 121 further includes another plurality of gates for shifting the first group parallel signals, wherein a Lth gate in the plurality of gates corresponding to a Lth parallel signal in the first group parallel signals is controlled by a (L−1)th sampling pulse of the N sampling pulses, and the Lth gate shifts the corresponding Lth parallel signal (L−1) times one clock cycle of the second clock domain, L being an integral between 1 and (N−S). Referring to FIG. 7A is a block diagram of a preferred exemplary embodiment of a circuit for transferring data stream in multiple clock domains with same frequency. A divider circuit (not shown) divides the pulses of clock domains D 251, D+1 252, D+2 253 into even sampling pulses CLK1 _(—) e 205, CLK2 _(—) e 208, CLK3 _(—) e 209 and odd sampling pulses CLK1 _(—) o 206, CLK2 _(—) o 207, CLK 3 _(—) o 210. The digital data stream DATA0 200 is then sampled by upper and lower routes respectively. In the upper route, the sampling circuits 21, 22 use sampling pulse CLK1 _(—) e 205 and sampling pulse CLK2 _(—) o 207 to sample the digital data stream DATA0 200, DATA1 201 in clock domains D+1 252, D+2 253 respectively. As same operation in the lower route, the sampling circuits 31, 32 use sampling pulse CLK1 _(—) o 206 and sampling pulse CLK2 _(—) e 208 to sample the digital data stream DATA0 200, DATA2 301 in clock domains D+1 250, D+2 253 respectively. At the end of in the clock domain D+3 254, the sampled signal DATA3 202, DATA4 203 from the upper route and lower route are then combined by the passing gates 23, 33 controlled by sampling pulse CLK3 _(—) e 209 and sampling pulse CLK 3 _(—) o 210 respectively to become series digital data DATA5 300.

Referring to FIG. 7B is a timing diagram of the sampling pulses in FIG. 3A in accordance with an embodiment of the present invention. In the upper route, since there is enough tolerance between the sample edge of sampling pulse CLK1 _(—) e 205 and sampling pulse CLK2 _(—) o 207, the skew or jitter in the sampling edge of sampling pulse CLK2 _(—) o 207 may not generate sampling ambiguity. In the lower route, since there is enough tolerance between the sample edge of sampling pulse CLK1 _(—) o 206 and sampling pulse CLK2 _(—) e 208, the skew or jitter in the sampling edge of sampling pulse CLK2 _(—) e 208 also may not generate sampling ambiguity.

Furthermore, the sampling pulses CLK1 _(—) e 205, CLK1 _(—) o 206, CLK2 _(—) e 208, CLK2 _(—) o 207, CLK3 _(—) e 209, and CLK3 _(—) o 210 used in the sampling circuits 21, 22, 31, 32 and the passing gates 23, 33 respectively have same frequency. The frequency of sampling pulse CLK1 _(—) e 205 plus sampling pulse CLK1 _(—) o 206 are equal the frequency of sampling pulse CLK1, and same relation exists in the sampling pulse CLK2 _(—) e 208 and the sampling pulse CLK2 _(—) o with the sampling pulse CLK2, the sampling pulse CLK3 _(—) e 209 and the sampling pulses CLK3 _(—) o 210 with the sampling pulse CLK3. Moreover, the both frequencies of sampling pulse CLK1 _(—) e 205 and sampling pulse CLK1 _(—) o 206 are same, and same relation exists in the sampling pulse CLK2 _(—) e 208 and the sampling pulse CLK2 _(—) o 207 with the sampling pulse CLK2, the sampling pulse CLK3 _(—) e 209 and the sampling pulse CLK3 _(—) o 210 with the sampling pulse CLK3. The phase difference between the sampling pulse CLK1 _(—) e 205 and the sampling pulse CLK1 _(—) o 206 is half of sampling pulse CLK1 _(—) e 205, and same relation exists in the sampling pulse CLK2 _(—) e 208 and the sampling pulse CLK2 _(—) o 207 with the sampling pulse CLK2, the sampling pulse CLK3 _(—) e 209 and the sampling pulse CLK3 _(—) o 210 with the sampling pulse CLK3.

Additionally, if N is an odd number, sampling circuits in the upper route sample the digital data stream with from first odd sampling pulse to (N−1)th even sampling pulse in odd-even sequence by turns, and the number of total sampling pulses is N−1, and sampling circuits in the lower route sample the digital data stream with from first even sampling pulse to (N−1)th odd sampling pulse in even-odd sequence by turns. The total sampling pulses is N−1. The combination circuit uses the Nth odd sampling pulse and the Nth even sampling pulse to sample both sampling signals in the upper route and in the lower route by turns, and then cross outputting series digital signal.

Furthermore, if N is an even number, sampling circuits in the upper route sample the digital data stream with from first odd sampling pulses to (N−1)th odd sampling pulses in odd-even sequence by turns, and the number of total sampling pulses is N−1; and sampling circuits in the lower route sample the digital data stream with from first even sampling pulse to (N−1)th even sampling pulses in even-odd sequence by turns, and the number of total sampling pulses is N−1. The combination circuit uses the Nth odd sampling pulse and the Nth even sampling pulse to sample both sampling signals by turns, and then cross outputting series digital signal.

Accordingly, referring the FIG. 8 depicts a flow chart of the method in accordance with an embodiment of the present invention. The digital data stream is in first clock domain in which there are first sampling pulse, second sampling pulse . . . (N−1)th sampling pulse and Nth sampling pulse. The digital data stream includes first digital signal, second digital signal . . . (N−1)th digital signal and Nth digital signal in parallel, and each digital signal corresponds to each sampling pulse in sequence. Step S31, dividing first pulse, second pulse . . . (N−1)th pulse and Nth pulse to generate some odd sampling pulses including first odd sampling pulse, second odd sampling pulse . . . (N−2)th odd sampling pulse and (N−1)th odd sampling pulse, and some even sampling pulses including first even sampling pulse, second even sampling pulse . . . (N−2)th even sampling pulse and (N−1)th even sampling pulse. Step S32, sampling the digital data stream with even sampling pulses and odd sampling pulses in even-odd sequence by turns, and then outputting a sampling signal. Step S33, sampling the digital data stream with odd sampling pulses and even sampling pulses in odd-even sequence by turns, and then outputting a sampling signal. Step S34, combining both of sampling signals to generate a series digital signal.

Additionally, if N is an odd number, the step S32, sampling circuits sample the digital data stream with from first odd sampling pulse to (N−1) even sampling pulse in odd-even sequence by turns, and the number of total sampling pulses is N−1; and step S33, sampling circuits sample the digital data stream with from first even sampling pulse to (N−1)th odd sampling pulse in even-odd sequence by turns. The total sampling pulses are N−1. In the step S34, the Nth pulse is divided into a Nth odd sampling pulse and a Nth even sampling pulse, and then the sampling signal is sampled with the Nth odd sampling pulse and another sampling signal is sampled with the Nth even sampling pulse by turns, and cross outputting a series digital signal at the end.

Furthermore, if N is an even number, the step S32, sampling circuits sample the digital data stream with from first odd sampling pulses to (N−1) odd sampling pulses in odd-even sequence by turns, and the number of total sampling pulses is N−1. The step S33, sampling circuits sample the digital data stream with from first even sampling pulse to (N−1)th even sampling pulse in even-odd sequence by turns, and the number of total sampling pulses is N−1. In the step S34, the Nth pulse is divided into a Nth odd sampling pulse and a Nth even sampling pulse and then the sampling signal is sampled with the Nth even sampling pulse and another sampling signal is sampled with Nth odd sampling pulses by turns, and cross outputting series digital signal at the end.

Referring to FIG. 9 is a block diagram of a preferred exemplary embodiment of a circuit for transferring data stream across multiple clock domains. The digital data stream includes three parallel bits (DATA10 601, DATA11 602, and DATA12 603). The bit DATA11 602 is sampled by sampling pulse SEL_1 701 in the sampling circuit 41 and then stored in the register 51 for shifting ⅓ period. The bit DATA12 603 is sampled by sampling pulse SEL_2 702 in the sampling circuit 41 and then stored in the register 52 for shifting ⅔ periods. Therefore, an intermediated clock domain is created by such preliminary sampling and shifting. The un-shifted data bit DATA10 601, the shifted data bit DATA13, and the shifted data bit DATA14 is then sampled by sampling pulses SEL_1 701, SEL_2 702, and SEL_0 700 in the sampling circuit 43, 44, 45 respectively and combined to become a series data stream DATA15 609. As a result, in referring FIG. 10, since there is enough tolerance for sampling pulse SEL_1 701 to sample data bit DATA10 602, sampling pulse SEL_2 702 to sample data bit DATA11 603, and sampling pulse SEL_0 700 to sample data bit DATA10 601, thus the sampling ambiguity will not happen.

Still continuing to refer FIG. 9, the phase difference between the shift data bit DATA 11 602 and the data bit DATA 13 604 is 1/N of the clock circle in first clock domain, and the phase difference between the shift data bit DATA12 603 and the data bit DATA14 605 is 2/N of the clock circle in first clock domain, N is total parallel number 3. Moreover, the sampling pulses SEL_0 700, SEL_1 701, SEL_2 702 have same frequency.

Accordingly, the FIG. 11 depicts a flow chart of the method in accordance with an embodiment of the present invention. The digital data stream is in first clock domain in which there is the first sampling pulse, second sampling pulse . . . (N−1)th sampling pulse and Nth sampling pulse. The digital data stream includes first digital signal, second digital signal . . . (N−1)th sampling pulse and Nth digital signal in parallel, and each digital signal corresponds to each sampling pulse in sequence. Step S41, shifting second digital signal, third digital signal . . . (N−1)th digital signal and Nth digital signal to produce second shift digital signal, third shift digital signal . . . (N−1)th shift digital signal and Nth shift digital signal, and step S42, sampling first shift digital signal, second shift digital signal . . . (N−1)th shift digital signal and Nth shift digital signal by second sampling pulse, third sampling pulse . . . Nth sampling pulse and first sampling pulse respectively, and outputting a series digital signal which is a low voltage differential signaling (LVDS) or reduced swing differential signaling (RSDS).

Accordingly, one embodiment of the present invention provides a effective data transfer circuit and method that allows digital data transferring multiple clock domains be sampled with plurality of sampling pulses. As a result, the unwanted data transferring error, such as phase difference and sampling ambiguity caused by skew and jitter may not happen.

Although the present invention has been explained in relation to its preferred embodiment, it is to be understood that other modifications and variation can be made without departing the spirit and scope of the invention as hereafter claimed. 

1. A method for transferring a data stream with N parallel signals from a first clock domain to a second clock domain, the N parallel signals having a first group parallel signals and a second group parallel signals, the N parallel signals being corresponding to a N sampling pulses with a first sequence, the method comprising: (a) shifting the second group parallel signal; and (b) sequentially sampling and outputting each signal in the first group parallel signals and the shifted second group digital signals by the N sampling pulses with a second sequence, wherein the second sequence is different from the first sequence.
 2. The method according to claim 1, the first sequence of N sampling pulses being a first to a (M−1)th sampling pulses and a Mth to a Nth sampling pulses, the second sequence of N sampling pulses being the Mth to the Nth sampling pulses and the first to the (M−1)th sampling pulses, wherein M is a first predetermined integral.
 3. The method according to claim 1, the second group parallel signals having S parallel signals, each signal in the second group parallel signals being shifted I times one clock cycle of the second clock domain in step (a), wherein I is a second predetermined integral.
 4. The method according to claim 3, the first group parallel signals having (N−S) parallel signals, the method further comprising: shifting each signal in the first group parallel signals before sampling the same in step (b), wherein a Lth parallel signal in the first group parallel signals is shifted (L−1) times one clock cycle in the second clock domain and L is an integral between 1 and (N−S).
 5. The method according to claim 1, the second group parallel signals having S parallel signals and each signal in the second group parallel signals being shifted in step (a), wherein a Kth parallel signal in the second group parallel signals being shifted (K+I−1) times one clock cycle of the second clock domain, and I is a second predetermined integral and K is an integral between 1 and S.
 6. The method according to claim 5, the first group parallel signals having (N−S) parallel signals, the method further comprising: shifting each signal in the first group parallel signals before sampling the same in step (b), wherein a Lth parallel signal in the first group parallel signals is shifted (L−1) times one clock cycle of the second clock domain and L is an integral between 1 and (N−S).
 7. A circuit for transferring a data stream with N parallel signals from a first clock domain to a second clock domain, the N parallel signals having a first group parallel signals and a second group parallel signals, the N parallel signals being corresponding to a N sampling pulses with a first sequence, the circuit comprising: a shifting circuit for shifting the second group parallel signals; and a sampling module for sequentially sampling and outputting each signal in the first group parallel signals and the shifted second group digital signals by the N sampling pulses with a second sequence, wherein the second sequence is different from the first sequence.
 8. The circuit according to claim 7, the first sequence of N sampling pulses being a first to a (M−1)th sampling pulses and a Mth to a Nth sampling pulses, the second sequence of N sampling pulses being the Mth to the Nth sampling pulses and the first to the (M−1)th sampling pulses, wherein M is a first predetermined integral.
 9. The circuit according to claim 7, the second group parallel signals having S parallel signals and the shifting circuit including a second plurality of gates corresponding to the second group parallel signals, each gate being controlled by an Ith sampling pulse of the N sampling pulses and each gate shifting the corresponding parallel signal I times one clock cycle of the second clock domain, wherein I is a second predetermined integral.
 10. The circuit according to claim 9, the first group parallel signals having (N−S) parallel signals, the shifting circuit further comprising: a first plurality of gates for shifting the first group parallel signals, wherein a Lth gate in the first plurality of gates corresponding to a Lth parallel signal in the first group parallel signals is controlled by a (L−1)th sampling pulse of the N sampling pulses, and the Lth gate shifts the corresponding Lth parallel signal (L−1) times one clock cycle of the second clock domain, L being an integral between 1 and (N−S).
 11. The circuit according to claim 7, the second group parallel signals having S parallel signals and the shifting circuit including a second plurality of gates corresponding to the second group parallel signals, wherein a Kth gate of the second plurality of gates is controlled by an (K+I−1)th sampling pulse of the N sampling pulses and the Kth gate shifts the corresponding parallel signal (K+I−1) times one clock cycle of the second clock domain, I being a second predetermined integral and K being an integral between 1 and S.
 12. The circuit according to claim 11, the first group parallel signals having (N−S) parallel signals, the shifting circuit further comprising: a first plurality of gates for shifting the first group parallel signals, wherein a Lth gate in the first plurality of gates corresponding to a Lth parallel signal in the first group parallel signals is controlled by a (L−1)th sampling pulse of the N sampling pulses, and the Lth gate shifts the corresponding Lth parallel signal (L−1) times one clock cycle of the second clock domain, L being an integral between 1 and (N−S).
 13. A method for transferring a set of (Q*N) serial digital data from a first clock domain with a first sampling clock to a second clock domain with a second sampling clock, the method comprising: (a) dividing the set of (Q*N) serial digital data and generating Q digital data streams; and (b) sequentially transferring the Q digital data streams to the second clock domain, each digital data stream including N parallel signals with a first group parallel signals and a second group parallel signals, the N parallel signals being corresponding to a N sampling pulses with a first sequence, each digital data stream being transferred by the following steps: (b1) shifting the second group parallel signal; and (b2) sequentially sampling and outputting each signal in the first group parallel signals and the shifted second group digital signals by the N sampling pulses with a second sequence, wherein the second sequence is different from the first sequence.
 14. The method according to claim 13, the first sequence of N sampling pulses being a first to a (M−1)th sampling pulses and a Mth to a Nth sampling pulses, the second sequence of N sampling pulses being the Mth to the Nth sampling pulses and the first to the (M−1)th sampling pulses, wherein M is a first predetermined integral.
 15. The method according to claim 13, the second group parallel signals having S parallel signals, each signal in the second group parallel signals being shifted a first amount equal to I times one clock cycle of the second clock domain in step (b1), wherein I is a second predetermined integral.
 16. The method according to claim 15, the first group parallel signals having (N−S) parallel signals, the method further comprising: shifting each signal in the first group parallel signals before sampling the same in step (b2), wherein a Lth parallel signal in the first group parallel signals is shifted a second amount equal to (L−1) times one clock cycle in the second clock domain and L is an integral between 1 and (N−S).
 17. The method according to claim 13, the second group parallel signals having S parallel signals and each signal in the second group parallel signals being shifted in step (b1), wherein a Kth parallel signal in the second group parallel signals being shifted a first amount equal to (K+I−1) times one clock cycle of the second clock domain, and I is a second predetermined integral and K is an integral between 1 and S.
 18. The method according to claim 17, the first group parallel signals having (N−S) parallel signals, the method further comprising: shifting each signal in the first group parallel signals before sampling the same in step (b2), wherein a Lth parallel signal in the first group parallel signals is shifted a second amount equal to (L−1) times one clock cycle of the second clock domain and L is an integral between 1 and (N−S).
 19. A circuit for transferring a set of (Q*N) serial digital data from a first clock domain with a first sampling clock to a second clock domain with a second sampling clock, the circuit comprising: a divider for dividing the set of (Q*N) serial digital data and generating Q digital data streams; and a transmitter for sequentially transferring each of the Q digital data streams to the second clock domain, each digital data stream including N parallel signals with a first group parallel signals and a second group parallel signals, the N parallel signals being corresponding to a N sampling pulses with a first sequence, the transmitter comprising: a shifting circuit for shifting the second group parallel signals; and a sampling module for sequentially sampling and outputting each signal in the first group parallel signals and the shifted second group digital signals by the N sampling pulses with a second sequence, wherein the second sequence is different from the first sequence.
 20. The circuit according to claim 19, the first sequence of N sampling pulses being a first to a (M−1)th sampling pulses and a Mth to a Nth sampling pulses, the second sequence of N sampling pulses being the Mth to the Nth sampling pulses and the first to the (M−1)th sampling pulses, wherein M is a first predetermined integral.
 21. The circuit according to claim 19, the second group parallel signals having S parallel signals and the shifting circuit including a second plurality of gates corresponding to the second group parallel signals, each gate being controlled by an Ith sampling pulse of the N sampling pulses and each gate shifting the corresponding parallel signal I times one clock cycle of the second clock domain, wherein I is a second predetermined integral.
 22. The circuit according to claim 21, the first group parallel signals having (N−S) parallel signals, the shifting circuit further comprising: a first plurality of gates for shifting the first group parallel signals, wherein a Lth gate in the first plurality of gates corresponding to a Lth parallel signal in the first group parallel signals is controlled by a (L−1)th sampling pulse of the N sampling pulses, and the Lth gate shifts the corresponding Lth parallel signal (L−1) times one clock cycle of the second clock domain, L being an integral between 1 and (N−S).
 23. The circuit according to claim 19, the second group parallel signals having S parallel signals and the shifting circuit including a second plurality of gates corresponding to the second group parallel signals, wherein a Kth gate of the second plurality of gates is controlled by an (K+I−1)th sampling pulse of the N sampling pulses and the Kth gate shifts the corresponding parallel signal (K+I−1) times one clock cycle of the second clock domain, I being a second predetermined integral and K being an integral between 1 and S.
 24. The circuit according to claim 23, the first group parallel signals having (N−S) parallel signals, the shifting circuit further comprising: a first plurality of gates for shifting the first group parallel signals, wherein a Lth gate in the first plurality of gates corresponding to a Lth parallel signal in the first group parallel signals is controlled by a (L−1)th sampling pulse of the N sampling pulses, and the Lth gate shifts the corresponding Lth parallel signal (L−1) times one clock cycle of the second clock domain, L being an integral between 1 and (N−S). 